1. Technical Field
The present invention relates, in general, to a portable computer system and a controlling method thereof and, more particularly, to a portable computer system and controlling method in which an LCD back light is automatically controlled.
2. Related Art
Generally, a portable computer system comprises a main body and a display apparatus. The main body includes hardware components such as a hard disk, memory cards, etc., a micom (micro control unit), and a power supplying unit for supplying electric power to the main body and the display apparatus. The display apparatus includes a liquid crystal display (LCD) panel rotatably joined to the main body by a hinge and displaying a picture thereon, and a back light illuminating the LCD panel.
The portable computer system is provided with a volume controller or a hot key controlling the brightness of the back light so as to control the brightness of a screen.
However, in the portable computer system, there may be a waste of electric power because the back light has a constant brightness regardless of the contrast of a video signal, and it is inconvenient for a user to control the brightness of the back light according to a change in contrast.
Thus, a further portable computer system has been developed, and is equipped with a smart module for sensing the contrast of the video signal displayed on the LCD panel, and for automatically controlling the brightness of the back light according to the contrast sensed by the smart module.
In the portable computer system equipped with the smart module, if a user sets the back light to a maximum state, the brightness of the back light is automatically controlled within the range of a minimum value through a maximum value according to the contrast of the video signal. If the user sets the back light to a typical state, the brightness of the back light is automatically controlled within the range of a minimum value through a typical value according to the contrast of the video signal.
However, in the portable computer system equipped with the smart module, a micom outputting a control signal for controlling the back light according to a user's control input is indirectly connected to an inverter via a direct current (DC) converter. Further, the control signal outputted from the micom is different from a control signal outputted from the smart module in a voltage range. Therefore, the control signal of the smart module may be not within the limits of an operating voltage of the inverter. In other words, the output impedance of the smart module may be different from the input impedance of the inverter.
Further, when a main body, in which the operating voltage of the inverter is set based on the voltage range of the smart module, is connected to a general LCD apparatus which is not equipped with a smart module, a voltage matching circuit is additionally required. Thus, the manufacturing process gets complicated and the cost of production increases.
Moreover, in the portable computer system equipped with the smart module, even if the contrast is changed rapidly, the brightness of the back light changes slowly.
The following are considered to be generally pertinent to the present invention but are burdened by the disadvantages set forth above: Korean Patent Publication No. 1998-26702 to Kyung-Soo Lee, entitled BRIGHTNESS CONTROL APPARATUS IN A LCD, published on 5 Aug. 1998; Korean Patent Publication No. 1999-84477 to Chang-Soo Shon, entitled METHOD AND CIRCUIT OF RIVING A BACK LIGHT IN A PORTABLE APPARATUS, published on 6 Dec. 1999; Japanese Patent Publication No. 5-165424 to Yano, entitled INVERTER FOR LCD BACK LIGHT, published on 2 Jul. 1993; Japanese Patent Publication No. 5-276656 to Hirayama et al., entitled LIQUID CRYSTAL DISPLAY, published on 22 Oct. 1993; Japanese Patent Publication No. 6-034946 to Shibata, entitled BACK LIGHT UNIT, published on 10 Feb. 1994; Japanese Patent Publication No. 7-120719 to Kanai, entitled LIGHT CONTROLLABLE DEVICE, published on 12 May 1995; Japanese Patent Publication No. 7-211476 to Nomoto, entitled LIGHTING CIRCUIT FOR FLUORESCENT LAMP, published on 11 Aug. 1995; Japanese Patent Publication No. 8-213182 to Lee, entitled DRIVING CIRCUIT OF REAR SURFACE LIGHT SOURCE OF LIQUID CRYSTAL DISPLAY ELEMENT, published on 20 Aug. 1996; Japanese Patent Publication No. 9-230304 to Iijima, entitled LIQUID CRYSTAL BACK LIGHT DRIVE CIRCUIT, published on 5 Sep. 1997; Japanese Patent Publication No. 9-080377 to Shikanuma, entitled DIMMER FOR IMAGE DISPLAY DEVICE, published on 28 Mar. 1997; Japanese Patent Publication No. 10-148808 to Kohata, entitled BACKLIGHT DEVICE AND LIQUID CRYSTAL DISPLAY DEVICE USING IT; Japanese Patent Publication No. 11-097196 to Nagai, entitled DIMMING DEVICE FOR LIQUID CRYSTAL DISPLAY, published on 9 Apr. 1999; U.S. Pat. No. 5,854,617 to Lee et al., entitled CIRCUIT AND A METHOD FOR CONTROLLING A BACKLIGHT OF A LIQUID CRYSTAL DISPLAY IN A PORTABLE COMPUTER, issued on Dec. 29, 1998; and U.S. Pat. No. 6,069,449 to Murakami, entitled BACKLIGHT CONTROL DEVICE FOR AN LCD, issued on May 30, 2000.